Viread: First Nucleotide Analogue Approved

Viread is the first nucleotide analogue available for HIV treatment approved by the FDA as a recommended antiretroviral agent for HIV. It was approved in October of 2001. Viread (also known as tenofovir) is a medication that looks as if it may be of use for people with resistance or problems with currently available nucleoside analogue drugs (nukes). Both nucleoside and nucleotide analogs inhibit the reverse transcriptase enzyme which translates the viral RNA into DNA, allowing the viral genetic message to be permanently inserted into the host cell. However, Viread, a nucleotide analog, is different from nucleoside analogue drugs because it is already in an activated form (phosphorylated), requiring one less activation step inside the cell to become an active compound.

The makers of the new nucleotide analogue Viread report that in two studies of treatment-experienced people, Viread demonstrated significant viral load reductions through 24 and 48 weeks. These studies were conducted in adults with HIV viral replication despite ongoing antiretroviral therapy.

Gilead Sciences reported results in treatment-experienced individuals at 72 weeks that looked promising as well. Adding once-a-day 300 mg Viread to a stable drug combination (called "drug intensification") quickly showed a significant viral load decrease in 92 heavily pre-treated people, which was maintained after a year, an average drop of 0.6 log. However, T-cells did not seem to be increased significantly.

Viread was successful in showing viral load decrease in people with nucleoside reverse transcriptase inhibitors resistance (NRTI). Epivir resistance seems to increase the effectiveness of Viread, at least in the test tube. Viread does not appear to have cross-resistance with other HIV medicines. Three percent of people developed the tenofovir-associated K65R resistance mutation after 48 weeks. Unlike the nucleosides, nucleotides can enter uninfected cells, and once there, protect against infection. In laboratory studies Viread seems not to cause mitochondrial toxicity, a problem associated with some of the other NRTI drugs.

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The body removes 70% to 80% of the drug through the kidneys. Because of the clearance through the kidneys, caution should be used in using Viread in someone with significantly decreased kidney function. However, Viread does not appear to cause any kidney damage, which its precursor drug, adefovir, was associated with. Overall, the tolerability of Viread is very good, with headaches and nausea being the most commonly reported side effects, and these symptoms tended to be mild. It is recommended that Viread be taken with a meal to increase the absorption of the drug.

Viread is an active agent against hepatitis B virus (HBV) and therefore may prove useful in HBV/HIV co-infected individuals, and Viread seems to have less reported toxicity in the liver than the majority of NRTIs.

Studies in antiretroviral-naive patients are ongoing in Phase IV trials; consequently, the risk-benefit has yet to be determined. There are no data demonstrating the effect of Viread on clinical progression of HIV. The use of Viread should be considered for treating adult patients with HIV strains that are expected to be susceptible to Viread as assessed by laboratory testing or treatment history. Viread was not approved for use in people without prior HIV treatment, but only for use in people with significant resistance to the NRTI class of drugs.

For more information about Viread use, call the STEP Talkline at (877) 597-STEP.

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